The projects under investigation are as follows: 1. The cell surface binding sites for fibronectin are being analyzed using monoclonal antibodies and cross-linking reagents developed under this project. We are also cloning the cDNAs encoding the receptor proteins. These binding sites are important in many cellular functions (adhesion, morphology, cytoskeletal organization, migration). Binding sites are exposed on platelets during hemostasis and may be altered in other cells by malignant transformation. 2. Fibronectin promotes cell migration and is apparently involved in this process during several phases of embryogenesis. Fibronectin first appears at gastrulation, and we have shown in amphibian embryos that it is encoded by a maternal mRNA. We are studying further the role of extracellular matrix in promoting and guiding cell migration in early embryos. (A)